| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Crater |
| Right ascension | 11h00m 33.85257s[2] |
| Declination | −18° 19′ 29.5827″[2] |
| Apparent magnitude (V) | 8.1 - 9.5[3] |
| Characteristics | |
| Evolutionary stage | AGB[4] |
| Spectral type | M7/8III[5] |
| Variable type | SRb[6] |
| Astrometry | |
| Radial velocity (Rv) | 20.94±1.50[2] km/s |
| Proper motion (μ) | RA: −29.373±0.180[2] mas/yr Dec.: −2.499±0.172[2] mas/yr |
| Parallax (π) | 4.7027 ± 0.1528 mas[2] |
| Distance | 690 ± 20 ly (213 ± 7 pc) |
| Details | |
| Mass | 1.91[7] M☉ |
| Radius | 633[8] R☉ |
| Luminosity | 8,151[8] L☉ |
| Surface gravity (log g) | −0.86[8] cgs |
| Temperature | 3,295[9] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
R Crateris is a star about 700 light years from the Earth in the constellation Crater. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days.[3] It is not visible to the naked-eye, but can be seen with a small telescope, or binoculars.[11] R Crateris is a double star; the variable star and its magnitude 9.9 F8V companion are separated by 65.4 arcseconds.[12]
Although the period for large brightness changes in R Crateris is listed as ~160 days, in 1982 Silvia Livi and Thaisa Bergmann reported small (~0.1 magnitude) variations on timescales of less than one hour. The rapid variations seem to be more regular when the star is near maximum brightness.[13]
R Crateris is an oxygen-rich asymptotic giant branch star, losing mass at a rate of 8×10−7 solar masses per year via a stellar wind.[4] At large distances from the star, the wind is expanding into space at 11.7±0.3 km/sec.[14]
Near-infrared radiation from R Crateris was detected in the first Two-Micron Sky Survey, published in 1969.[15] It was detected in the far-infrared by the IRAS satellite, and that emission was resolvedbyIRAS, showing that the star is surrounded by a large circumstellar shell containing dust.[16] High resolution far-infrared images of R Crateris taken by the Herschel Space Observatory show that the emitting region of the shell, roughly 280 arcseconds (0.94 light year) across, consists primarily of two non-concentric arcs well separated from the star itself. The arcs are probably bowshocks formed as the dusty stellar wind collides with the interstellar medium.[17] The total mass of the shell, including both dust and gas, is estimated to be about (6.4±2)×10−2 solar masses.[18] Infrared imaging of the innermost (sub-arcsecond) portion of the dust shell shows a bipolar structure.[4][19]
In the early 1970s, maser emission from OH and H2O was detected in R Cratoris' circumstellar shell.[20] SiO maser emission was detected in 1985.[21] Thermal (non-maser) emission from CO was detected in 1986.[22]
With the high angular resolution provided by Very Long Baseline Interferometry, the H2O maser emission is seen to arise from small (milli-arcsecond) blobs, whose proper motions through the inner region of the circumstellar shell can be measured. These observations give additional evidence that R Cratoris has developed a bipolar stellar wind.[23]
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